From: Alexander Weps <exander77@pm.me>
To: Rich Felker <dalias@libc.org>
Cc: musl@lists.openwall.com, Daniel Gutson <danielgutson@gmail.com>,
Markus Wichmann <nullplan@gmx.net>
Subject: Re: [musl] Broken mktime calculations when crossing DST boundary
Date: Sun, 24 Mar 2024 19:06:58 +0000 [thread overview]
Message-ID: <3yixwTENdfygkyC-VpJQ3EN-X6RgOM_A9EYuLzX0CgM_wOfDncIPUkyoj7RQkfdPk_IvYOo6gNwao8cHNiWkNoZoa8DhvJk3i0fYp1mC1fU=@pm.me> (raw)
In-Reply-To: <9c2qfe36CoPBfKjzn1lDDZ_hfyNJCZW6-6ZTZlQgHAPr2djicIMMweEqUoQoQsDWsBt4AAZBL8vZlcsVCL950rYhcPpMDvhzDWean3oVHbs=@pm.me>
I ran Asia/Omsk from 1900 to 2200 there and back again (59 seconds increments/decrements).
Everything ok in glibc.
Fails in musl very early:
1919-11-13 23:59:32 LMT
1919-11-13 23:54:01 LMT
No idea what is even happening there.
Glibc shows nothing interesting there:
1911-12-13 23:59:32 LMT
1911-12-14 00:00:31 LMT
???
AW
On Sunday, March 24th, 2024 at 19:36, Alexander Weps <exander77@pm.me> wrote:
> It is tiring, because you are not correct.
>
> You are also talking about a slightly different thing.
>
> If you have normalized time T1 in struct tm and you add something, normalize, you should always get normalized time T2, what is higher than T1.
> If you have normalized time T2 in struct tm and you subtract something, normalize, you should always get normalized time T1, which is lower than T2.
>
> I agree than for non normalized time (tm_isdst = -1 etc.) this would not apply. I agree that the decision how to deduce it is implementation specific and I don't really hold it against musl. I rewrote everything without tm_isdst = -1.
>
> But there cannot be a case where you have normalized time add something, normalize and create normalized time that is lower and vice versa.
>
> If you claim otherwise, provide counter example.
>
> I have done pretty extensive testing.
>
> AW
>
>
>
> On Sunday, March 24th, 2024 at 19:24, Rich Felker dalias@libc.org wrote:
>
> > On Sun, Mar 24, 2024 at 06:16:20PM +0000, Alexander Weps wrote:
> >
> > > > And subtracting seconds can't make time go forwards, but that's
> > > > what would happen with the alternate interpretation you want.
> > >
> > > That's just nonsense.
> > >
> > > I can go from 1900 to 2200 by adding seconds.
> > > And from 2200 to 1900 by subtracting seconds.
> > >
> > > I just did that using glibc.
> > >
> > > This is because each addition to struct tz fields leads to time
> > > going forward and each subtraction from struct tz fields leads to
> > > time going backwards.. As it should.
> > >
> > > There is clear ordering of struct tz contents.
> >
> > This is getting really tiring.
> >
> > In the presence of times which do not exist, the properties you want
> > are not mathematically consistent.
> >
> > EITHER you get cases where "start from time T, add something,
> > normalize" gives a broken-down time that looks like it's before T (but
> > isn't, because it's in a different zone rule),
> >
> > OR you get cases where "start from time T, subtract something,
> > normalize" gives a broken-down time that looks like it's after T (bit
> > isn't, because it's in a different zone rule).
> >
> > Preferring one of these nasty behaviors over the other is entirely
> > arbitrary.
> >
> > Time zones are nasty. Local time is nasty. If you want to do things
> > with it, you have to deal with that nastiness.
> >
> > Rich
next prev parent reply other threads:[~2024-03-24 19:07 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-24 13:36 Alexander Weps
2024-03-24 16:59 ` Alexander Weps
2024-03-24 17:04 ` Rich Felker
2024-03-24 17:12 ` Alexander Weps
2024-03-24 18:00 ` Alexander Weps
2024-03-24 18:02 ` Rich Felker
2024-03-24 18:16 ` Alexander Weps
2024-03-24 18:24 ` Rich Felker
2024-03-24 18:36 ` Alexander Weps
2024-03-24 19:01 ` Joakim Sindholt
2024-03-24 19:05 ` Alexander Weps
2024-03-24 19:06 ` Alexander Weps [this message]
2024-03-24 19:13 ` Alexander Weps
2024-03-24 19:13 ` Alexander Weps
2024-03-24 19:22 ` Rich Felker
2024-03-24 19:57 ` Alexander Weps
2024-03-24 20:22 ` Rich Felker
2024-03-24 20:50 ` Alexander Weps
2024-03-24 21:43 ` Alexander Weps
2024-03-24 23:51 ` Thorsten Glaser
2024-03-25 0:36 ` Alexander Weps
2024-03-25 11:52 ` Alexander Weps
2024-03-25 12:21 ` Rich Felker
2024-03-25 12:55 ` Alexander Weps
2024-03-25 13:08 ` Rich Felker
2024-03-25 13:13 ` Alexander Weps
2024-03-25 13:13 ` Rich Felker
2024-03-25 13:24 ` Alexander Weps
2024-03-25 13:42 ` Rich Felker
2024-03-25 13:48 ` Alexander Weps
2024-03-25 13:50 ` Alexander Weps
2024-03-25 18:02 ` Rich Felker
2024-03-25 18:28 ` Alexander Weps
2024-03-25 18:53 ` Rich Felker
2024-03-25 18:57 ` Alexander Weps
2024-03-25 19:38 ` Rich Felker
2024-03-25 19:47 ` Rich Felker
2024-03-25 20:05 ` Alexander Weps
2024-03-25 20:12 ` Alexander Weps
2024-03-25 20:00 ` Alexander Weps
2024-03-25 20:23 ` Rich Felker
2024-03-25 20:31 ` Rich Felker
2024-03-25 23:19 ` Thorsten Glaser
2024-03-25 23:16 ` Thorsten Glaser
2024-03-25 13:44 ` Alexander Weps
2024-03-25 22:40 ` Thorsten Glaser
2024-03-25 22:59 ` Alexander Weps
2024-03-25 23:34 ` Thorsten Glaser
2024-03-26 12:45 ` Alexander Weps
2024-03-26 21:59 ` Thorsten Glaser
2024-03-27 0:14 ` Alexander Weps
2024-03-27 0:38 ` Alexander Weps
2024-03-27 1:35 ` Thorsten Glaser
2024-03-27 2:45 ` Alexander Weps
2024-03-27 4:42 ` Thorsten Glaser
2024-03-26 18:56 ` Alexander Weps
2024-03-25 23:13 ` Rich Felker
-- strict thread matches above, loose matches on Subject: below --
2024-03-22 19:56 Alexander Weps
2024-03-23 6:41 ` Markus Wichmann
[not found] ` <528SeRFaPfDw7fA4kqKDlio1U4RB_t9nmUemPcWw9_t1e2hBDpXYFmOqxAC37szgYvAVtmTuXWsmT64SSN3cSQFVdrQqXUAgkdTMPZQ0bg0=@pm.me>
2024-03-23 10:38 ` Markus Wichmann
2024-03-23 11:59 ` Alexander Weps
2024-03-23 12:00 ` Alexander Weps
2024-03-23 12:31 ` Rich Felker
2024-03-23 13:49 ` Alexander Weps
2024-03-23 15:31 ` Rich Felker
2024-03-23 16:54 ` Alexander Weps
2024-03-23 18:57 ` Alexander Weps
2024-03-23 19:33 ` Alexander Weps
2024-03-23 20:18 ` Rich Felker
2024-03-23 20:40 ` Alexander Weps
2024-03-24 0:36 ` Eric Pruitt
2024-03-24 2:04 ` Rich Felker
2024-03-24 3:32 ` Daniel Gutson
2024-03-24 11:05 ` Alexander Weps
2024-03-24 13:24 ` Alexander Weps
2024-03-23 12:01 ` Alexander Weps
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